For raising the tank, you can very easily raise it ~1" (IIRC). I think to go more and you have to move it above the rear frame cross-section. Take a look at how it's mounted to the frame. There is a drop on the rear mount that is shorter the the two drops on the front edge. Cut the rear off and grind flat, then reweld to the frame. Cut the fronts off and trim to equal the amount cut off the rear.

I did this with my original 2" BL. I have since cut the BL in half and there were no clearance inssues with the tank.

I did extend my gas filler hose. I had a second hose from a parts truck. I used a section of it, spliced with galvanize exhaust pipe, and clamped up.